Method and apparatus for receiving ACK/NACK in wireless communication system

ABSTRACT

The present invention provides a method for receiving acknowledgement/not-acknowledgement (ACK/NACK) of a terminal in a wireless communication system. The method transmits uplink data through an uplink data channel and receives ACK/NACK for the uplink data. The uplink data channel is transmitted through aggregated carriers and the aggregated carriers include a first band recognizable to first and second type terminals and a second band recognizable only to the second type terminal.

This application is a 35 USC §371 National Stage entry of InternationalApplication No. PCT/KR2013/008640 filed on Sep. 26, 2013, and claimspriority to U.S. Provisional Application No. 61/706,093 filed on Sep.26, 2012; 61/723,310 filed on Nov. 6, 2012; 61/729,345 filed on Nov. 22,2012; 61/753,921 filed on Jan. 17, 2013 and 61/763,937 filed on Feb. 12,2013, all of which are hereby incorporated by reference in theirentireties as if fully set forth herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to wireless communication, and moreparticularly, to a method and apparatus for receivingacknowledgement/not-acknowledgement (ACK/NACK) indicating a receptionconfirmation in a wireless communication system.

2. Related Art

One of the most important requirements of a next generation wirelesscommunication system is to support a high data rate. For this, varioustechniques such as multiple input multiple output (MIMO), cooperativemultiple point transmission (CoMP), relay, etc., have been underresearch, but the most fundamental and reliable solution is to increasea bandwidth.

However, a frequency resource is in a saturation state at present, andvarious schemes are partially used in a wide frequency band. For thisreason, in order to ensure a broadband bandwidth to satisfy a requiredhigher data rate, a system is designed such that a basic requirementwhich allows separate bands to operate respective independent systems issatisfied, and a carrier aggregation (CA) is introduced. In concept, theCA aggregates a plurality of bands into one system. In this case, a bandthat can be independently managed is defined as a component carrier(CC).

The latest communication standard (e.g., 3GPP LTE-A or 802.16m)considers to expand its bandwidth to 20 MHz or higher. In this case, awideband is supported by aggregating one or more CCs. For example, ifone CC corresponds to a bandwidth of 5 MHz, four carriers are aggregatedto support a bandwidth of up to 20 MHz. As such, a system supportingcarrier aggregation is called a carrier aggregation system.

Meanwhile, the wireless communication system considers a system in whichmore terminals are supported by one base station in comparison with thelegacy system. For example, due to a technique such as machine typecommunication (MTC), enhanced multi user multi input multi output(MIMO), etc., there may be a need to support more terminals by one basestation.

In this case, it may be difficult to transmit control information tomultiple terminals when using only the conventional control channel fortransmitting control information, for example, a physical downlinkcontrol channel (PDCCH) in long term evolution (LTE). This is because aproblem may occur in which a radio resource of the PDCCH is not enoughor an interference is severe. To solve such a problem, it is consideredto allocate a new control channel in a radio resource region in whichdata is transmitted in the legacy system. Such a new control channel iscalled an enhanced-PDCCH (E-PDCCH). When using the E-PDCCH, how todetermine a starting position of the E-PDCCH may be a matter to beconsidered.

Meanwhile, a base station transmits acknowledgement/not-acknowledgement(ACK/NACK) for uplink data received from the terminal through a physicalhybrid-ARQ indicator channel (PHICH). The PHICH is located in a regionto which a PDCCH, i.e., the legacy control channel, is allocated. ThePHICH may also have a problem in which a radio resource is insufficientor an interference occurs if the number of terminals supported by thebase station is increased and a carrier aggregation is supported.Therefore, it is considered to introduce a channel for new ACK/NACKtransmission, and such a channel is called an enhanced-PHICH (E-PHICH).

Meanwhile, in a future wireless communication system, it is consideredto use a carrier having a new channel structure which is not compatiblewith the legacy wireless communication system. Such a carrier ishereinafter called a new carrier type (NCT). A carrier used in thelegacy wireless communication system is called a legacy carrier type(LCT). The future wireless communication system considers a carrieraggregation which aggregates the LCT and the NCT. In this case, how todetermine a resource for transmitting ACK/NACK by a base station may bea matter to be considered.

SUMMARY OF THE INVENTION

A method and apparatus for receiving acknowledgement/not-acknowledgement(ACK/NACK) in a wireless communication system are provided.

In an aspect, a method of receiving acknowledgement/not-acknowledgement(ACK/NACK) of a terminal in a wireless communication system is provided.The method comprises transmitting uplink data through an uplink datachannel and receiving ACK/NACK for the uplink data. The uplink datachannel is transmitted through aggregated carriers, and the aggregatedcarriers include a first band recognizable to first and second typeterminals and a second band recognizable only to the second typeterminal.

In another aspect, a terminal is provided. The terminal comprises aradio frequency (RF) unit for transmitting and receiving a radio signaland a processor operatively coupled to the RF unit. The processor isconfigured for transmitting uplink data through an uplink data channeland receiving acknowledgement/not-acknowledgement (ACK/NACK) for theuplink data. The uplink data channel is transmitted through aggregatedcarriers, and the aggregated carriers include a first band recognizableto first and second type terminals and a second band recognizable onlyto the second type terminal.

According to the present invention, a carrier aggregation system caneffectively perform ACK/NACK transmission for a plurality of cells. Inaddition, an E-PDCCH region or a PDSCH region can be effectivelyconfigured.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a structure of a frequency division duplex (FDD)radio frame in a 3GPP LTE.

FIG. 2 illustrates a structure of a time division duplex (TDD) radioframe in a 3GPP LTE.

FIG. 3 illustrates an example of a resource grid with respect to onedownlink slot.

FIG. 4 illustrates a downlink subframe.

FIG. 5 illustrates a structure of an uplink subframe.

FIG. 6 illustrates a synchronization HARQ.

FIGS. 7(a) and 7(b) illustrate an example of comparing an existingsingle carrier system and a carrier aggregation system.

FIG. 8 shows a structure of a PHICH in 3GPP LTE.

FIG. 9 shows an example of configuring an E-PHICH region and an E-PDCCHregion.

FIG. 10 shows an example of a structure of a carrier including asegment.

FIGS. 11(A)-11(D) show an example of PUSCH indexing methods.

FIG. 12 shows an example of configuring an uplink band when a bandincluding a segment is configured as a downlink band.

FIG. 13 shows a method of determining a starting position of an E-PDCCH.

FIG. 14 shows a structure of a BS and a UE according to an embodiment ofthe present invention.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Long term evolution (LTE) of the 3^(rd) generation partnership project(3GPP) standard organization is a part of an evolved-universal mobiletelecommunications system (E-UMTS) using an evolved-universalterrestrial radio access network (E-UTRAN). The LTE employs anorthogonal frequency division multiple access (OFDMA) in a downlink andemploys single carrier-frequency division multiple access (SC-FDMA) inan uplink. LTE-advance (LTE-A) is an evolution of the LTE. For clarity,the following description will focus on the 3GPP LTE/LTE-A. However,technical features of the present invention are not limited thereto.Hereinafter, terminologies of “a first radio access technology (RAT)”and “a second RAT” may be used. The second RAT provides backwardcompatibility with the first RAT in some frequency bands among systembands, but may not provide backward compatibility in the remainingfrequency bands. The second RAT may be an evolution of the first RAT.

User Equipment (UE) may be fixed or mobile, and may be called otherterms such as an MS (mobile station), an MT (mobile UE), a UT (user UE),an SS (subscriber station), a wireless device, a PDA (personal digitalassistant), a wireless modem, a handheld device, and the like.

Generally, a base station means a fixed station communicating with theUE, and may be called as other terms such as an eNB (evolved-NodeB), aBTS (Base Transceiver System), and an Access Point.

A wireless device may be served by a plurality of serving cells. Eachserving cell may be defined with a downlink (DL) component carrier (CC)or a pair of the DL CC and an uplink (UL) CC. Hereinafter, the CC isalso simply referred to as a carrier.

The serving cell may be classified into a primary cell and a secondarycell. The primary cell operates at a primary frequency, and is a celldesignated as the primary cell when an initial network entry process isperformed or when a network re-entry process starts or in a handoverprocess. The primary cell is also called a reference cell. The secondarycell operates at a secondary frequency. The secondary cell may beconfigured after a radio resource control (RRC) connection isestablished, and may be used to provide an additional radio resource. Atleast one primary cell is configured always. The secondary cell may beadded/modified/released by using higher-layer signaling (e.g., a radioresource control (RRC) message).

A cell index (CI) of the primary cell may be fixed. For example, alowest CI may be designated as a CI of the primary cell. It is assumedhereinafter that the CI of the primary cell is 0 and a CI of thesecondary cell is allocated sequentially starting from 1.

FIG. 1 illustrates a structure of a frequency division duplex (FDD)radio frame in a 3GPP LTE. The structure of a frequency division duplex(FDD) radio frame may refer to a fourth section of 3GPP TS 36.211 V8.7.0(2009-05) “Evolved Universal Terrestrial Radio Access (E-UTRA); PhysicalChannels and Modulation (Release 8)”.

The radio frame includes 10 subframes marked with indexes of 0˜9. Onesubframe includes two continuous slots. A time required to transmit onesubframe is a TTI (transmission time interval). For example, a length ofone subframe may be 1 ms (milli-second), and a length of one slot may be0.5 ms.

FIG. 2 shows a time division duplex (TDD) radio frame in 3GPP LTE.

In the TDD radio frame, a downlink (DL) subframe, an uplink (UL)subframe, and a special subframe may coexist.

Table 1 below shows an example of a UL-DL configuration of a radioframe.

TABLE 1 UL-DL configura- Switch-point Subframe index tion periodicity 01 2 3 4 5 6 7 8 9 0 5 ms D S U U U D S U U U 1 5 ms D S U U D D S U U D2 5 ms D S U D D D S U D D 3 10 ms  D S U U U D D D D D 4 10 ms  D S U UD D D D D D 5 10 ms  D S U D D D D D D D 6 5 ms D S U U U D S U U D ‘D’denotes a DL subframe, ‘U’ denotes a UL subframe, and ‘S’ denotes aspecial subframe. Upon receiving the UL-DL configuration from a BS, a UEcan know which subframe is a DL subframe or a UL subframe according to aradio frame configuration.

A subframe having an index #1 and an index #6 may be a special subframe,and includes a downlink pilot time slot (DwPTS), a guard period (GP),and an uplink pilot time slot (UpPTS). The DwPTS is used in a UE forinitial cell search, synchronization, or channel estimation. The UpPTSis used in a BS for channel estimation and uplink transmissionsynchronization of the UE. The GP is a period for removing interferencewhich occurs in an uplink due to a multi-path delay of a downlink signalbetween the uplink and a downlink.

FIG. 3 illustrates an example of a resource grid with respect to onedownlink slot.

Referring to FIG. 3, a downlink slot includes a plurality of OFDMsymbols in a time domain and N_(RB) Resource Blocks (RBs) in a frequencydomain. The RB includes one slot in the time domain in a resourceallocation unit, and a plurality of continuous sub-carriers in afrequency domain. The number N_(RB) of RBs included in the downlink slotdepends on a downlink transmission bandwidth set in a cell. For example,the number N_(RB) of RBs in the LTE system may be one of 6 to 110. Astructure of the uplink slot may be the same as a structure of thedownlink slot.

Meanwhile, each element on the resource grid is a resource element (RE).The resource element on the resource grid may be identified by an indexpair (k,l) in a slot. In this case, a k (k=0, . . . , N_(RB)×12−1)represents a sub-carrier index, and l(l=0, . . . , 6) represents an OFDMsymbol index in the slot.

Although FIG. 3 has illustrated that one RB is configured by 7 OFDMsymbols in a time domain and 12 sub-carriers in a frequency domain toinclude 7×12 resource elements, and the number of OFDM symbols and thenumber of sub-carriers in the RB are not limited thereto. A 1 slot in anormal CP may include 7 OFDM symbols, and a 1 slot in an extended CP mayinclude 6 OFDM symbols. The number of the OFDM symbols and the number ofthe sub-carriers may be variously changed according to a length of theCP, a frequency spacing, and the like. One of 128, 256, 512, 1024, 1536,and 2048 may be selectively used as the number of sub-carriers in oneOFDM symbol.

FIG. 4 illustrates a downlink subframe.

A downlink (DL) subframe is divided into a control region and a dataregion in a time region. The control region include maximum 4 OFDMsymbols before a first slot in a subframe, but the number of OFDMsymbols included in the control region may be changed. A PDCCH (PhysicalDownlink Control Channel) and other control channel are allocated to thecontrol region, and a PDSCH is allocated to the data region.

As disclosed in 3GPP TS 36.211 V 10.2.0, a physical control channel in a3GPP LTE/LTE-A includes a PDCCH (Physical Downlink Control Channel), aPCFICH (Physical Control Format Indicator Channel), and a PHICH(Physical Hybrid-ARQ Indicator Channel).

A PCFICH transmitted from a first OFDM symbol of the subframe transfersa CFI (control format indicator) regarding the number of OFDM symbols(that is, a size of the control region) used to transmit controlchannels in the subframe. A wireless device firstly receives a CFI onthe PCFICH, and then monitors the PDCCH.

Unlike the PDCCH, the PCFICH does not use blind decoding, but istransmitted through a fixed PCFICH resource of the subframe.

The PHICH transfers ACK(acknowledgement)/NACK(not-acknowledgement)signals for uplink (UL) HARQ (hybrid automatic repeat request) process.The ACK/NACK signals regarding UL data on the PUSCH transmitted by theUE are transmitted on the PHICH by the base station.

A PBCH (Physical Broadcast Channel) is transmitted from four OFDMsymbols before a second slot of a first subframe of the radio frame. ThePBCH transfers essential system information to communicate with the basestation, and the system information transmitted through the PBCH refersto MIB (master information block). Meanwhile, system informationtransmitted on a PDSCH indicated by the PDCCH refers to an SIB (systeminformation block).

Control information transmitted through the PDCCH refers to downlinkcontrol information (DCI). The DCI may include resource allocation ofthe PDSCH (refers to DL grant (downlink grant) or DL assignment (DLassignment)), resource allocation of PUSCH (refers to UL grant), a setof transmission power control commands and/or activation of VoIP (Voiceover Internet Protocol) with respect to individual UEs in apredetermined UE group.

The usage of the DCI format can be classified as shown in Table 2 below.

TABLE 2 DCI format Usage DCI format 0 It is used for PUSCH scheduling.DCI format 1 It is used for scheduling of one PDSCH codeword. DCI format1A It is used for compact scheduling and random access process of onePDSCH codeword. DCI format 1B It is used in simple scheduling of onePDSCH codeword having precoding information. DCI format 1C It is usedfor very compact scheduling of one PDSCH codeword. DCI format 1D It isused for simple scheduling of one PDSCH codeword having precoding andpower offset information. DCI format 2 It is used for PDSCH schedulingof UEs configured to a closed-loop spatial multiplexing mode. DCI format2A It is used for PDSCH scheduling of UEs configured to an open-loopspatial multiplexing mode. DCI format 3 It is used for transmission of aTPC command of a PUCCH and a PUSCH having a 2-bit power adjustment. DCIformat 3A It is used for transmission of a TPC command of a PUCCH and aPUSCH having a 1-bit power adjustment. DCI format 4 It is used for PUSCHscheduling in one UL cell in a multi-antenna transmission mode.

Transmission of a DL transmission block in a 3GPP LTE/LTE-A is performeda pair of the PDCCH and the PDSCH. Transmission of a UL transmissionblock is performed a pair of the PDCCH and the PDSCH. For example, thewireless device receives a DL transmission block on a PDSCH indicated bythe PDCCH. The wireless device monitors the PDCCH in a DL subframe, andreceives DL resource assignment on the PDCCH. The radio device receivesa DL transmission block on a PDSCH indicated by the DL resourceassignment.

The base station determines a PDCCH format according to a DCT to be sentto the wireless device to attach a CRC (Cyclic Redundancy Check) to aDCI, and masks unique identifier (refers to RNTI (Radio NetworkTemporary Identifier) according an owner or an application the PDCCH toCRC.

In a case of a PDCCH for a specific wireless device, an uniqueidentifier of the wireless device, for example, a C-RNTI (Radio NetworkTemporary Identifier) may be masked to the CRC. Alternatively, in a caseof a PDCCH for a paging message, a paging indication identifier, forexample, a P-RNTI (Paging-RNTI) may be masked to the CRC. In a case of aPDCCH for system information, system information identifier, that is,SI-RNTI (system information-RNTI) may be masked to the CRC. In order toindicate a random access response being a response to transmission ofthe random access preamble, RA-RNTI (random access-RNTI) may be maskedto the CRC. So as to indicate a TPC (transmit power control) commandwith respect to a plurality of wireless devices, TPC-RNTI may be maskedto the CRC. In a PDCCH for semi-persistent scheduling (SPS), SPS-C-RNTImay be masked to the CRC.

If C-RNTI is used, the PDCCH transfer control information (refers toUE-specific control information) for a corresponding specific wirelessdevice. If other RNTI is used, the PDCCH transfers common controlinformation received by all or a plurality of wireless devices in acell.

A DCI to which the CRC is added is encoded to generate coded data.Encoding includes channel encoding and rat matching. The coded data aremodulated to generate modulated symbols. The modulated symbols aremapped to a physical RE (resource element).

The control region in the subframe includes a plurality of controlchannel elements (CCEs). The CCE is a logical allocation unit used toprovide a coding rate according to a state of a wireless channel to thePDCCH, and corresponds to a plurality of resource element groups (REGs).The REG includes a plurality of resource elements (REs). According tothe relationship between the number of CCEs and a coding rate providedby the CCEs, a format of the PDCCH and the bit number of possible PDCCHsare determined.

One REG includes four REs, and one CCE includes 9 REGs. In order toconfigure one PDCCH, {1, 2, 4, 8} CCE may be used. Each element of {1,2, 4, 8} refers to a CCE aggregation level.

The base station determines the number of CCEs used to transmit thePDDCH is determined according to a channel state. For example, one CCEmay be used to transmit the PDCCH in a wireless device having anexcellent downlink channel state. 8 CCEs may be used to transmit thePDCCH in a wireless device having a poor downlink channel state.

A control channel configured by one or more CCEs performs interleavingof an REG unit, and is mapped to a physical resource after cyclic shiftbase a cell ID is performed.

The 3GPP LTE uses blind decoding for PDCCH detection. The blind decodingis a scheme in which a desired identifier is de-masked from a CRC of areceived PDCCH (referred to as a candidate PDCCH) to determine whetherthe PDCCH is its own control channel by performing CRC error checking. Awireless device cannot know about a specific position in a controlregion in which its PDCCH is transmitted and about a specific CCEaggregation or DCI format used for PDCCH transmission.

A plurality of PDCCHs can be transmitted in one subframe. The wirelessdevice monitors the plurality of PDCCHs in every subframe. Herein,monitoring is an operation of attempting PDCCH decoding by the wirelessdevice according to a format of the monitored PDCCH.

The 3GPP LTE uses a search space to reduce a load of blind decoding. Thesearch space can also be called a monitoring set of a CCE for the PDCCH.The wireless device monitors the PDCCH in the search space.

The search space is classified into a common search space and aUE-specific search space. The common search space is a space forsearching for a PDCCH having common control information and consists of16 CCEs having CCE indices 0 to 15, and supports a PDCCH having a CCEaggregation level of {4, 8}. However, a PDCCH (e.g., DCI formats 0, 1A)for carrying UE-specific information can also be transmitted in thecommon search space. The UE-specific search space supports a PDCCHhaving a CCE aggregation level of {1, 2, 4, 8}.

FIG. 5 illustrates a structure of an uplink subframe.

Referring to FIG. 5, the uplink subframe may be divided into a controlregion and a data region in a frequency region. A PUCCH (Physical UplinkControl Channel) for transmitting uplink control information isallocated to the control region. A PUSCH (Physical Uplink SharedChannel) for transmitting data (control information may be transmittedtogether with the data in some cases) is allocated to the data region.The UE may simultaneously transmit the PUCCH and the PUSCH or maytransmit only one of the PUCCH and the PUSCH according to setting.

The PUCCH with respect to one UE is allocated as a RB pair in asubframe. RBs belonging to the RB pair have different sub-carriers in afirst slot and a second slot, respectively. A frequency of an RBbelonging to the RB pair allocated to the PUCCH is changed based on aslot boundary. This means that a frequency of an RB pair allocated tothe PUCCH is hopped in a slot boundary. The uplink control informationis transmitted through different sub-carriers according to a time sothat a frequency diversity gain may be obtained.

Hybrid automatic repeat request (HARQ), acknowledgment(ACK)/non-acknowledgement (NACK), channel state information (CSI)indicating a downlink channel state, for example, a channel qualityindicator (CQI), a precoding matrix index (PMI), a precoding typeindicator (PTI), a rank indication (RI), etc., may be transmitted on aPUCCH.

<Semi-Persistent Scheduling: SPS>

In the wireless communication system, the UE receives schedulinginformation such as DL grant and UL grant through a PDCCH to perform anoperation of transmitting the PUSCH. In general, the DL grant and thePDSCH are received in the same subframe. Further, in a case of the FDD,the PUSCH is transmitted after fourth subframes from a subframereceiving the UL grant. An LTE except for the dynamic schedulingprovides semi-persistent scheduling (SPS).

Downlink or uplink SPS may report by which subframe semi-statictransmission (PUSCH)/reception (PDSCH) is performed to the UE through ahigher layer signal. For example, a parameter give as the higher layersignal may be a period and an offset value of the subframe.

The UE recognizes SPS transmission/reception through RRC signaling. Ifreceiving activation and release signal of SPS transmission through thePDCCH, the UE performs or releases SPS transmission/reception. That is,although an SPS is allocated through RRC signaling, when SPStransmission/reception are not performed but the activation or releasesignal is received through the PDCCH, frequency resource (resourceblock) according to a resource block allocation designated in the PDCCHand modulation and a coding rate according to MCS information areapplied so that SPS transmission/reception are performed in a subframecorresponding to a subframe period and an offset value allocated throughRRC signaling. If an SPS release signal is received through the PDSSH,SPS transmission/reception stop. If a PDCCH (SPS reactivation PDCCH)including an SPS activation signal is again received, the stopped SPStransmission/reception restarts using a frequency resource and an MCSdesignated by a corresponding PDCCH. Hereinafter, a PDCCH for SPSactivation is called SPS activation PDCCH, and a PDCCH for SPS releaseis called an SPS release PDCCH.

<HARQ (Hybrid Automatic Repeat Request)>

Upon transmission/reception of data between the base station and the UE,when the frame is not received or damaged, an error control methodincludes an ARQ (Automatic Repeat request) scheme and a HARQ (hybridARQ) scheme which is a developed scheme thereof. In the ARQ scheme,after one frame is transmitted, a confirmation message ACK is waitedfor. Only when a reception side exactly receives the frame, thereception side sends the confirmation message ACK. When an error occursin the frame, the reception side sends a NACK (negative-ACK) message,and a reception frame with the error removes the information in areceiving end buffer. When the transmission side receives the ACKsignal, the transmission side transmits a next frame. When receive theNACK message, the transmission side retransmits the frame.

Unlike the ARQ scheme, according to the HARQ scheme, when the receivedframe cannot be demodulated, a receiving end transmits an NACK messageto the transmitting end. However, when the received frame is stored inthe buffer for a predetermined time so that the frame is retransmitted,the frame is coupled with the received frame so that a reception successrate is increased.

In recent years, more efficient HARQ scheme than the ARQ scheme may bewidely used. There are various types of HARQ schemes. The HARQ schememay be divided into synchronous HARQ and asynchronous HARQ according toretransmission timing. The HARQ scheme may be divided into achannel-adaptive scheme and a channel-non-adaptive scheme according topresence of reflection of a channel state with respect to an amount of aresource used upon retransmission.

FIG. 6 shows an example of synchronization HARQ.

In a synchronization HARQ scheme, subsequent retransmission is achievedat a timing determined by a system when initial transmission fails. Thatis, if it is assumed that a timing at which retransmission is achievedafter initial transmission is every 8^(th) time unit (subframe), sincethis is agreed in advance between a BS and a UE, there is no need toadditionally report this timing. However, if a NACK message is receivedin a data transmission side, data is retransmitted in the every 8^(th)time unit until an ACK message is received.

The UE transmits a UL transport block on a PUSCH 320 by using an initialUL grant in an (n+4)^(th) subframe.

The BS sends an ACK/NACK signal for the UL transport block on a PHICH331 in an (n+8)^(th) subframe. The ACK/NACK signal indicates a receptionacknowledgement for the UL transport block. The ACK signal indicates areception success, and the NACK signal indicates a reception failure.When the ACK/NACK signal is the NACK signal, the BS may send aretransmission UL grant on a PDCCH 332, or may not send an additional ULgrant. Alternatively, retransmission of previous data may be suspendedand a UL grant may be sent for transmission of new data. In case the ACKsignal, the BS may send the UL grant for new transmission through thePDCCH. In addition, the BS may send the UL grant for retransmission (orretransmission UL grant). Upon receiving the retransmission UL grant,the UE ignores the ACK/NACK signal and follows an instruction of theretransmission UL grant. This is because the UL grant has higherreliability since the ACK/NACK signal does not have CRC and the UL granthas CRC.

When the UL grant is not received and the NACK signal is received, thewireless device sends a retransmission block on a PUSCH 340 in an(n+12)^(th) subframe. For the transmission of the retransmission block,if the retransmission UL grant is received on the PDCCH 332, thewireless device uses the received retransmission UL grant, and if theretransmission UL grant is not received, the wireless device uses thepreviously received UL grant.

The BS sends an ACK/NACK signal for the UL transport block on a PHICH351 in an (n+16)^(th) subframe. When the ACK/NACK signal is the NACKsignal, the BS may send a retransmission UL grant on a PDCCH 352, or maynot send an additional UL grant.

After initial transmission is performed in the (n+4)^(th) subframe,retransmission is performed in the (n+12)^(th) subframe, and thussynchronous HARQ is performed with an HARQ period corresponding to 8subframes.

On the other hand, the asynchronous HARQ scheme may be achieved by newlyscheduling a retransmission timing or through additional signaling. Atiming at which a retransmission of previously failed data is achievedvaries by several factors such as a channel state or the like.

The channel-non-adaptive HARQ scheme is a scheme in which datamodulation used in retransmission, the number of resource blocks, acoding scheme, or the like is determined as determined in the initialtransmission. Unlike this, the channel-adaptive HARQ scheme is a schemein which the data modulation used in retransmission, the number ofresource blocks, the coding scheme, or the like vary depending on achannel state.

For example, in the channel-non-adaptive HARQ scheme, a transmittingside transmits data by using 6 resource blocks in the initialtransmission, and the 6 resource blocks are also used in theretransmission.

On the other hand, in the channel adaptive HARQ scheme, even if data isinitially transmitted by using the 6 resource blocks, the data isretransmitted by using more (or less) than 6 resource blocks accordingto a channel state.

According to this classification, four HARQ combinations can beachieved. Examples of an HARQ scheme used in general include anasynchronous and channel-adaptive HARQ scheme and a synchronous andchannel-non-adaptive HARQ scheme. The asynchronous and channel-adaptiveHARQ scheme can maximize retransmission efficiency by adaptively varyinga retransmission timing and an amount of resources in use according to achannel state, but is not considered in general for an uplink sincethere is a disadvantage in that a signaling overhead is great.Meanwhile, the synchronous and channel-non-adaptive HARQ scheme has anadvantage in that there is almost no signaling overhead since aretransmission timing and a resource allocation are agreed in a system,but has a disadvantage in that retransmission efficiency is very lowwhen it is used in a channel state which varies significantly.

At present, the 3GPP LTE uses the asynchronous HARQ scheme in a downlinkcase and uses a synchronous HARQ scheme in an uplink case.

Meanwhile, in a downlink case for example, after data is transmittedthrough scheduling, a time delay occurs as shown in FIG. 6 until nextdata is transmitted again after information of ACK/NAK is received froma UE. This is a delay which occurs due to a channel propagation delayand a time required for data decoding and data encoding. To achieveseamless data transmission without being affected by such a delayduration, a transmission method using an independent HARQ process isused.

For example, if a minimum period between current data transmission andnext data transmission is 8 subframes, seamless data transmission can beachieved by preparing 8 independent processes. In LTE FDD, up to 8processes can be allocated if it does not operate in MIMO.

<Carrier Aggregation>

Now, a carrier aggregation system is described.

FIGS. 7(a) and 7(b) show an example of comparing the legacy singlecarrier system and a carrier aggregation system.

Referring to FIGS. 7(a) and 7(b), the single carrier system supportsonly one carrier as to a UE in an uplink and a downlink. Although thecarrier may have various bandwidths, only one carrier is assigned to theUE. Meanwhile, multiple component carriers (CCs), i.e., DL CCs A to Cand UL CCs A to C, can be assigned to the UE in the carrier aggregation(CA) system. The CC implies a carrier used in the CA system, and may besimply referred to as a carrier. For example, three 20 MHz CCs can beassigned to allocate a 60 MHz bandwidth to the UE.

The carrier aggregation system can be divided into a contiguous carrieraggregation system in which carriers are contiguous to each other and anon-contiguous carrier aggregation system in which carriers areseparated from each other. Hereinafter, when it is simply called thecarrier aggregation system, it should be interpreted such that bothcases of contiguous CCs and non-contiguous CCs are included.

A CC which is a target when aggregating one or more CCs may directly usea bandwidth that is used in the legacy system in order to providebackward compatibility with the legacy system. For example, a 3GPP LTEsystem may support a carrier having a bandwidth of 1.4 MHz, 3 MHz, 5MHz, 10 MHz, 15 MHz, and 20 MHz, and a 3GPP LTE-A system may configure awideband of 20 MHz or higher by using each carrier of the 3GPP LTEsystem as a CC. Alternatively, the wideband may be configured bydefining a new bandwidth without having to directly use the bandwidth ofthe legacy system.

A system frequency band of the wireless communication system isclassified into a plurality of carrier-frequencies. The carrierfrequency means a center frequency of a cell. Hereinafter, the cell maymean a downlink frequency resource and an uplink frequency resource.Alternatively, the cell may mean a combination of the downlink frequencyresource and an optional uplink frequency resource. Further, generally,when the CA is not considered, one cell may include a pair of uplink anddownlink frequency resources.

In order to transmit/receive packet data through the specific cell, theUE should finish configuration with specific cell. In this case, theconfiguration means a state of finishing reception of system informationnecessary to transmit/receive data with respect to a corresponding cell.For example, the configuration may include the whole procedure toreceive common physical layer parameters necessary to transmit/receivedata, or MAC (media access control) layer parameters, or parametersnecessary for a specific operation at an RRC layer. If a cell in whichthe configuration is terminated receives only information indicatingthat packet data may be transmitted, the cell may transmit and receive apacket at once.

The cell in which the configuration is terminated may be in anactivation state or a deactivation state. In this case, the activationmeans that data are transmitted or received or transmission or receptionof the data in a ready state. The UE may monitor or receive a controlchannel PDCCH and a data channel PDSCH of an activated cell in order toconfirm resources (frequency, time, or the like) allocated to the UE.

The deactivation means that transmission or reception of traffic data isimpossible and measurement or transmission/reception of minimuminformation is possible. The UE may receive system information SInecessary to receive a packet from a deactivated cell. Meanwhile, the UEdoes not monitor or receive a control channel PDCCH and a data channelPDSCH of the deactivated cell in order to confirm resources (frequency,time, or the like).

The cell may be classified into a primary cell, a secondary cell, and aserving cell.

The primary cell means a cell operating at a primary frequency, andmeans a cell performing initial connection establishment procedure orconnection reestablishment procedure with the base station or a cellindicated as a primary cell at a handover procedure.

The secondary cell means a cell operating in a secondary cell. If RRCconnection is established, the secondary cell is used to provide anadditional preset wireless resource.

In a case of UE in which the CA is not set or does not provide the CA,the serving cell is configured by the primary cell. When the carrieraggregation is set, the term ‘serving cell’ represents a cell set to theUE and a plurality of serving cell may be configured. One serving cellmay be configured by one downlink component carrier or a pair of{downlink component carrier, uplink component carrier}. A plurality ofserving cells may be configured by a primary cell and one secondary cellor a plurality of secondary cells.

A PCC (primary component carrier) signifies a component carrier (CC)corresponding to a primary cell. The PCC is a CC where the UE initiallyachieves connection or RRC connection with the base station among aplurality of CCs. The PCC is a special CC to provide connection or RRCconnection for signaling regarding a plurality of CC, and to manage UEcontext which is connection information associated with the UE. Further,when the PCC accesses the UE in an RRC connection mode, the PCC isalways in an active state. A downlink component carrier corresponding tothe primary cell refers to a DownLink Primary Component Carrier (DL PCC)and an uplink component carrier corresponding to the primary cell refersto an uplink primary component carrier (UL PCC).

The SCC (secondary component carrier) means a CC corresponding to thesecondary cell. That is, the SCC is a CC allocated to the UE except fora PCC. The SCC is an extended carrier when the UE selects for additionalresource allocation except for the PCC, and may be divided into aactivation state or a deactivation state. A downlink component carriercorresponding to the secondary cell refers to a DownLink secondaryComponent Carrier (DL SCC) and an uplink component carrier correspondingto the second cell refers to an uplink secondary component carrier (ULSCC).

The primary cell and the secondary cell have following characteristics.

First, the primary cell is used to transmit the PUCCH. Second, theprimary cell is always activated, but the second cell is a carrier whichis activated/deactivated according to a specific condition. Third, whenthe primary cell experiences a Radio Link Failure (hereinafter referredto as ‘RLF’). Fourth, the primary cell may be changed according tovariation in a security key, a RACH (Random Access CHannel) procedure,and an accompanying handover procedure. Fifth, NAS (non-access stratum)information is received through the primary cell. Sixth, in a case of anFDD system, the primary cell always configures a pair of the DL PCC andthe UL PCC. Seventh, different component carriers CCs may be set as theprimary cell every UE. Eighth, the primary cell may be replaced by onlyhandover, cell selection/cell reselection procedures. In addition of anew secondary cell, RRC signal may be used to transmit systeminformation of a dedicated secondary cell.

In a component carrier configuring the serving cell, the downlinkcomponent carrier may configure one serving cell, or the downlinkcomponent carrier and the uplink component carrier are connected andconfigured so that one serving cell may be configured. However, theserving cell may not be configured by only one uplink component carrier.

Activation/deactivation of the component carrier is similar to conceptof activation/deactivation of the serving cell. For example, activationof the serving cell 1 means activation of the DL CC1 on the assumptionthat the serving cell 1 is configured by a DL CC1. If the activation ofthe serving cell 2 means activation of a DL CC2 and the UL CC2 on theassumption that the serving cell 2 is configured by connecting andconfiguring a DL CC2 and a UL CC2. In this meaning, each componentcarrier may correspond to a serving cell.

The number of component carriers aggregated between downlink and uplinkmay be differently set. When the number of CCs in the downlink is thesame as the number of CCs in the uplink, the aggregation is symmetric.When the number of CCs in the downlink is different from the number ofCCs in the uplink, the aggregation is asymmetric. Further, the sizes(that is, bandwidths) of the CCs may be different from each other. Forexample, when five CCs is used to configure 70 MHz band, 5 MHzCC(carrier #0)+20 MHz CC(carrier #1)+20 MHz CC(carrier #2)+20 MHzCC(carrier #3)+5 MHz CC(carrier #4) may be configured.

As described above, the CA system may support a plurality of CCs, thatis, a plurality of serving cells unlike the single carrier system.

Such a CA system may support cross-carrier scheduling. The cross-carrierscheduling is a scheduling method capable of performing resourceallocation of a PDSCH transmitted through a different component carrierthrough a PDCCH transmitted through a specific component carrier and/orresource allocation of a PUSCH transmitted through other componentcarrier except for a component carrier fundamentally linked with thespecific component carrier. That is, the PDCCH and the PDSCH may betransmitted through different DL CCs, a PUSCH may be transmitted througha UL CC different from a UL CC liked with a DL CC to which a PDCCHincluding an UL is transmitted. As described above, in a system forsupporting the cross-carrier scheduling, the PDCCH needs a carrierindicator indicating that PDSCH/PUSCH are transmitted through a certainDL CC/UL CC. Hereinafter, a field including the carrier indicator refersto a carrier indication field (CIF).

A CA system to support the cross-carrier scheduling may include acarrier indicator field (CIF) included in a DCI (downlink controlinformation) format according to the related art. In the system tosupport the cross-carrier scheduling, for example, an LTE-A system,since a CIF is added to an existing DCI format (that is, a DCI formatused in an LTE), 3 bits may be spread, and a PDCCH structure may reusean existing coding method, a resource allocation method (that is, a CCEbased resource mapping).

The base station may set a PDCCH monitoring DL CC (monitoring CC) group.The PDCCH monitoring DL CC group is configured by a part of allaggregated DL CCs. If the cross-carrier scheduling is configured, the UEperforms PDCCH monitoring/decoding for only a DL CC included in thePDCCH monitoring DL CC group. That is, the base station transmits aPDCCH with respect to PDSCH/PUSCH to be scheduled through only the DLCCs included in the PDCCH monitoring DL CC group. The PDCCH monitoringDL CC group may be configured to UE-specific, UE group-specific, orcell-specific.

Non-cross carrier scheduling implies that scheduling information anddata depending thereon are transmitted/received in the same carrier(cell), and is also called self-scheduling.

FIG. 8 shows a structure of a PHICH in 3GPP LTE.

One PHICH carries only 1-bit ACK/NACK corresponding to a PUSCH for oneUE, that is, corresponding to a single stream.

In step S310, the 1-bit ACK/NACK is coded into 3 bits by using arepetition code having a code rate of 1/3.

In step S320, the coded ACK/NACK is modulated using binary phase shiftkeying (BPSK) to generate 3 modulation symbols.

In step S330, the modulation symbols are spread by using an orthogonalsequence. A spreading factor (SF) is N^(PHICH) _(SF)=4 in a normal CP,and is N^(PHICH) _(SF)=2 in an extended CP. The number of orthogonalsequences used in the spreading is N^(PHICH) _(SF)*2 to apply I/Qmultiplexing. PHICHs which are spread by using N^(PHICH) _(SF)*2orthogonal sequences can be defined as one PHICH group.

Table 3 below shows an orthogonal sequence for the PHICH.

TABLE 3 orthogonal sequence sequence index normal CP extended CP n^(seq)_(PHICH) (N^(PHICH) _(SF) = 4) (N^(PHICH) _(SF) = 2) 0 [+1 +1 +1 +1] [+1+1] 1 [+1 −1 +1 −1] [+1 −1] 2 [+1 +1 −1 −1] [+j +j] 3 [+1 −1 −1 +1] [+j−j] 4 [+j +j +j +j] 5 [+j −j +j −j] 6 [+j +j −j −j] 7 [+j −j −j +j]

In step S340, layer mapping is performed on the spread symbols.

In step S350, the layer-mapped symbols are transmitted by being mappedto resources.

A plurality of PHICHs mapped to resource elements of the same setconstitute a PHICH group. Each PHICH included in the PHICH group isidentified by a different orthogonal sequence. In the FDD system,N^(group) _(PHICH), i.e., the number of PHICH groups, is constant in allsubframes, and can be determined by Equation 1 below.

$\begin{matrix}{N_{PHICH}^{group} = \left\{ \begin{matrix}\left\lceil {N_{g}\left( {N_{RB}^{DL}/8} \right)} \right\rceil & {{for}\mspace{14mu}{normal}\mspace{14mu}{cyclic}\mspace{14mu}{prefix}} \\{2 \cdot \left\lceil {N_{g}\left( {N_{RB}^{DL}/8} \right)} \right\rceil} & {{for}\mspace{14mu}{extended}\mspace{14mu}{cyclic}\mspace{14mu}{prefix}}\end{matrix} \right.} & \left\lbrack {{Equation}\mspace{14mu} 1} \right\rbrack\end{matrix}$

Herein, Ng denotes a parameter transmitted through a physical broadcastchannel (PBCH), where Ngε{⅙,½,1,2}. N^(DL) _(RB) denotes the number ofDL RBs. ceil(x) is a function for outputting a minimum value amongintegers equal to or greater than x. floor(x) is a function foroutputting a maximum value among integers equal to or less than x.

The wireless device identifies a PHICH resource by using an index pair(n^(group) _(PHICH), n^(seq) _(PHICH)) used by the PHICH. A PHICH groupindex n^(group) _(PHICH) has a value in the range of 0 to N^(group)_(PHICH)−1. An orthogonal sequence index n^(seq) _(PHICH) denotes anindex of an orthogonal sequence.

An index pair (n^(group) _(PHICH), n^(seq) _(PHICH)) is obtainedaccording to Equation 2 below.n _(PHICH) ^(group)=(I _(PRB) _(_) _(RA) ^(lowest) ^(_) ^(index) +n_(DMRS))mod N _(PHICH) ^(group) +I _(PHICH) N _(PHICH) ^(group)n _(PHICH) ^(seq)=(└I _(PRB) _(_) _(RA) ^(lowest) ^(_) ^(index) /N_(PHICH) ^(group) ┘+n _(DMRS))mod 2N _(SF) ^(PHICH)  [Equation 2]

Herein, n_(DMRS) denotes a cyclic shift of a demodulation referencesignal (DMRS) within the most recent UL grant for a transport blockrelated to corresponding PUSCH transmission. The DMRS is an RS used forPUSCH transmission. N^(PHICH) _(SF) denotes an SF size of an orthogonalsequence used in PHICH modulation. I^(lowest) ^(_) ^(index) _(PRB) _(_)_(RA) denotes the smallest PRB index in a 1^(st) slot of correspondingPUSCH transmission. I_(PHICH) is 0 or 1.

A physical resource block (PRB) is a unit frequency-time resource fortransmitting data. One PRB consists of a plurality of contiguous REs ina frequency-time domain. Hereinafter, the RB and the PRB are used forthe same concept.

In a radio frame used in time division duplex (TDD), the number of PHICHgroups may change variously between downlink subframes. The number ofPHICH groups may be given as m_(i)·N^(group) _(PHICH), and m_(i) may begiven as shown in Table 4 below. Further, N^(group) _(PHICH) is given asshown in Equation 1 above, and an index n^(group) _(PHICH) ranges from 0to m_(i)·N^(group) _(PHICH)−1 in a downlink subframe having a PHICHresource.

TABLE 4 Uplink-downlink Subframe number i configuration 0 1 2 3 4 5 6 78 9 0 2 1 — — — 2 1 — — — 1 0 1 — — 1 0 1 — — 1 2 0 0 — 1 0 0 0 — 1 0 31 0 — — — 0 0 0 1 1 4 0 0 — — 0 0 0 0 1 1 5 0 0 — 0 0 0 0 0 1 0 6 1 1 —— — 1 1 — — 1

Meanwhile, a PHICH duration is configured by a higher layer, and may beconfigured as shown in Table 5 below.

TABLE 5 Non-MBSFN subframes Subframes 1 and 6 in MBSFN subframes PHICHcase of frame structure on a carrier duration type 2 All other casessupporting PDSCH Normal 1 1 1 Extended 2 3 2

Now, the present invention will be described.

In a system enhanced from LTE release 10, a greater number of UEs canaccess to one BS in comparison with the legacy system due to a techniquesuch as machine type communication (MTC), enhanced multi user-multiinput multi output (MU-MIMO), etc. In this case, it may be difficult todeliver control information to a plurality of UEs by using only theexisting control region, i.e., a PDCCH region, in a DL subframe. Thatis, the control region may be insufficient. In addition, a plurality ofRRHs or the like are deployed in a cell, which may cause a problem of aninterference in the control region.

The LTE-A system considers to introduce a new control channel to solve aresource shortage problem of a PDCCH which is a channel for transmittingcontrol information and a reception performance deterioration problem ofa PDCCH region caused by an interference. For convenience ofexplanation, the new control channel is called an enhanced-PDCCH(E-PDCCH).

The conventional PDCCH differs from the E-PDCCH as follows.

1) The conventional PDCCH may be located in a control region in asubframe, that is, a region consisting of first N OFDM symbols (where Nis any natural number in the range of 1 to 4), whereas the E-PDCCH maybe located in a data region in the subframe, that is, a regionconsisting of the remaining OFDM symbols other than the N OFDM symbols.

2) The conventional PDCCH can be decoded on the basis of a cell-specificreference signal, i.e., CRS, that can be received by all UEs in a cell,whereas the E-PDCCH can be decoded on the basis of not only the CRS butalso a DM-RS which is specific to a particular UE. Therefore, similarlyto the PDSCH, beamforming can be applied to the E-PDSCH by usingprecoding, and as a result, a reception SINR may be increased.

3) The conventional PDCCH may be applied to a UE which operates in LTE,whereas the E-PDCCH may be selectively applied to a UE supporting LTE-A.Of course, the UE supporting the LTE-A may also support the conventionalPDCCH.

In terms of resources constituting the E-PDDCH, there may be adistributed E-PDCCH consisting of distributed resources and a localizedE-PDCCH consisting of localized resources. The distributed E-PDCCH canacquire a diversity gain and can be used to transmit control informationfor several UEs. The distributed E-PDCCH has a frequency selectiveproperty and can be used to transmit control information for aparticular UE.

Meanwhile, in the LTE-A, a greater amount of ACK/NACK may be transmittedand an interference may become severe in comparison with the legacysystem such as a multi-node system in which multiple nodes are includedin a cell, a carrier aggregation system supporting multiple carriers,etc. Therefore, a PHICH may also have a resource shortage problem and areception performance deterioration problem caused by an interference.To solve these problems, the LTE-A considers to introduce a new PHICH inaddition to the conventional PHICH. For convenience of explanation, thenew PHICH is called an enhanced-PHICH (E-PHICH). The PHICH and theE-PHICH are channels on which a BS transmits ACK/NACK for a UL datachannel transmitted by a UE. Unlike a case where the PHICH is configuredin the PDCCH region, the E-PHICH may be configured in the PDSCH region.For example, the E-PHCIH may be configured in the E-PDCCH regionconfigured in the PDSCH region.

FIG. 9 shows an example of configuring an E-PHICH region and an E-PDCCHregion.

Referring to FIG. 9, the E-PDCCH region may be configured in a PDSCHregion.

Similarly to the PDCCH region, the E-PDCCH region may include anenhanced-common search space (E-CSS) in which all UEs or a specific UEgroup in a cell search for an E-PDCCH thereof and anenhanced-UE-specific search space (E-USS) in which only a specific UEsearches for an E-PDCCH thereof. Alternatively, only one of the E-CSSand the E-USS may be included.

Meanwhile, the E-PHICH may be configured in the E-PDCCH region. Forexample, the E-PHICH may be configured in the E-CSS. In this case, theE-PHICH may be used to transmit ACK/NACK for a plurality of UEs throughmultiplexing.

<Selection of PHICH or E-PHICH and Selection of Cell for ACK/NACK forPUSCH>

Even if both of the PHICH and the E-PHICH are supported in a wirelesscommunication system, only one of the PHICH and the E-PHICH may beconfigured for each cell or for each subframe, or both of them may beconfigured.

If the PHICH and the E-PHICH can be configured in the subframe, the UEmay monitor both of the PHICH and the E-PHICH to receive ACK/NACK for aPUSCH, which may be ineffective and may increase power consumption ofthe UE.

Hereinafter, for convenience of explanation, from a perspective of theUE, a cell for monitoring the PDCCH is called a PDCCH cell, a cell formonitoring the E-PDCCH is called an E-PDCCH cell, a cell fortransmitting the PHICH is called a PHICH cell, and a cell fortransmitting the E-PHICH is called an E-PHICH cell.

The PDCCH cell may be a cell in which a search space is configured inthe PDCCH region, and the E-PDCCH cell may be a cell in which the searchspace is configured in the E-PDCCH region. The PDCCH cell and theE-PDCCH cell may be mutually exclusive or may overlap with each other.The PHICH cell and the E-PHICH cell also may be mutually exclusive ormay overlap with each other. That is, in one cell, the UE may beconfigured to monitor the PHICH in some subframes, and the UE may beconfigured to monitor the E-PHICH in other subframes. That is, anoperation described below may differ for each subframe.

Now, a case where monitoring of an E-PHICH is not configured and a casewhere monitoring of the E-PHICH is configured are described belowdistinctively.

I. When it is configured that a UE does not monitor an E-PHICH.

1. First Embodiment

In a case where a UL grant exists in a PDCCH.

1) A corresponding PDCCH cell is a PHICH cell. That is, a PHICH istransmitted together in a cell in which the PDCCH is transmitted.Alternatively, 2) the PHICH cell may be designated with RRC. That is, aBS may configure a cell in which the PHICH is transmitted to a UEthrough an RRC message. In this case, the PHICH cell and the PDCCH cellmay be configured independently. This may be preferable for aconsistency for a case of designating a PHICH transmission cell by usingRRC as to an E-PDCCH cell.

2. Second Embodiment

In a case where a UL grant exists in an E-PDCCH.

1) Embodiment 2-1

When a plurality of cells are configured to a UE, a PDCCH cell among theplurality of cells may be a PHICH cell. If the PDCCH cell is plural innumber, the PHICH cell may be a primary cell.

Since a cell having a relatively good channel state is selected as thePDCCH cell, the PHICH cell is selected from PDCCH cells so that the UEcan reliably receive the PHICH. In particular, since the primary cellperforms decoding of a PDCCH region in system information reception andinitial access, a cell which is examined for PDCCH reception isselected.

2) Embodiment 2-2

A PHICH cell may be a cell in which a UL grant is transmitted through anE-PDCCH. That is, a BS may transmit a PHICH through a cell in which theUL grant is transmitted. This will be described with reference to FIG.13. In this manner, cell planning may be well achieved such that aninterference of a PDCCH region in which a PHICH is transmitted is notsevere in a cell which transmits a control channel or such that aninterference between different cells is excluded according to a featureof the PHICH which is shifted on a frequency axis on the basis of a cellID. This method may perform an operation irrelevant to reconfigurationof RRC signaling in terms of utilizing a PHICH resource of an activatedcell in which the control channel is transmitted.

3) Embodiment 2-3

A PHICH cell for a PUSCH may be pre-designated with RRC.

This method may decrease a PHICH transmission load concentrated in aprimary cell. If a plurality of NCT cells (cells in which a PHICHresource is not present) are configured in one UE, a PHICH cell appliedcommonly to all NCT cells may be designed through one RRC signaling.Alternatively, the PHICH cell may be designated for each NCT cell.

In addition, this method may be more effective in a sense that an LCTcell more suitable for an NCT cell can be selected when an aggregationis achieved between the NCT cell and the LCT cell. In case of asynchronization cell, an indirect indication is possible when areference cell is indicated with RRC.

Meanwhile, a cell designated as a PHICH cell for a PUSCH of another cellmay be restricted. For example, it may be restricted only to a cell formonitoring a PDCCH among a plurality of cells. This is because a ULgrant is scheduled to a PDCCH for a cell which operates in theconventional way as to a corresponding cell, and thus monitoring of anadditional PHICH region is not necessary, whereas if a cell other than aPDCCH monitoring cell is designated as a PHICH cell, a PHICH resource ofa cell designated as the PHICH cell must be additionally decoded.

Meanwhile, if a cell configured for the PDCCH monitoring is deactivated,monitoring of the PDCCH region stops. In this case, the situation may behandled as an exception so that the cell is designated as a PHICH celland monitoring of the PHICH is continued, or it may be restricted suchthat a cell configured to a PHICH cell for a PUSCH of another cell isalways activated.

4) Embodiment 2-4

Unlike methods of transmitting ACK/NACK through a PHICH, a PHICH for aPUSCH may not be transmitted. In this case, retransmission using HARQmay be performed only by using a UL grant. Conventionally, if there isno UL grant when NACK is received through the PHICH, a UE retransmits aPUSCH through a resource by using a previous UL grant. However, thepresent invention may not allow HARQ retransmission using NACK, and mayallow HARQ retransmission only using a UL grant.

The UE may determine whether to transmit a new PUSCH or retransmit aPUSCH on the basis of a new data indicator (NDI) included in the ULgrant. That is, if the NDI of the UL grant indicates new PUSCHtransmission, it may be assumed that the UE receives ACK for apreviously transmitted PUSCH. This method corresponds to a case ofoperating with synchronization HARQ.

Meanwhile, asynchronous HARQ may be applied as a method for allowingonly transmission using a UL grant. For this, a field indicating a ULHARQ process number may be added to the UL grant. Such an operation maybe applied only for an NCT in which a PDCCH does not exist.

A PDCCH and a PHICH may not exist in a new carrier type (NCT). In thiscase, the embodiments 2-1, 2-3, and 2-4 may be applied. In the NCT, todecrease the conventional CRS overhead, a channel may be estimated byusing a UE-specific RS and physical channel demodulation may beperformed. Therefore, a PDCCH and PHICH for performing demodulation byestimating a channel on the basis of the CRS may not be used in the NCT.In addition, in the existing legacy carrier type (LCT), the embodiment2-2 may be applied.

In case of the embodiments 2-2 and 2-3, if a corresponding cell is not aprimary cell, a PHICH may be configured by using a cell ID signaled withRRC, the number of reference signal antenna ports, Ng, and a PHICHduration.

The embodiment 2-2 may be configured when an E-PDCCH cell in which a ULgrant is transmitted is a PDCCH cell.

In addition, a PHICH may be used in case of a UL HARQ process scheduledwith a PDCCH and a PHICH-less operation may be used in case of a UL HARQprocess scheduled with an E-PDCCH, that is, the embodiment 2-4 may beused. Alternatively, the embodiment 2-2 may be used if a subframe forreceiving a retransmission UL grant is a subframe configured withmonitoring of a USS of a PDCCH, and the embodiment 2-1, 2-3, or 2-4 maybe applied if it is a subframe configured with monitoring of a USS of anE-PDCCH and the E-PHICH does not exist in the subframe.

The embodiments 2-1, 2-3, and 2-4 may be more suitable for a new carriertype (NCT) in which a CRS is not configured and thus cannot configure aPHICH. For example, if the E-PDCCH is transmitted in the NCT, since thePHICH cannot be configured in the NCT, the method of the embodiment 2-2cannot be used, and the aforementioned method is required.

II. Third Embodiment

In a case where a UE is configured to monitor an E-PHICH.

If the E-PHICH is configured through a higher layer signal, a PHICH andthe E-PHICH may exist simultaneously in the same subframe. Therefore, aBS may report to the UE about which channel is used to transmit ACK/NACKbetween the PHICH and the E-PHICH. A selective use of the PHICH and theE-PHICH depends on respective features thereof. In case of the PHICH, itmay be difficult to avoid performance deterioration if it is located ina PDCCH region and thus an interference of the PDCCH region is severe ina neighboring cell, whereas in case of the E-PHICH, an inter-cellinterference can be avoided since it may be configured in a PDSCHregion. On the other hand, an additional PDSCH resource is consumed inthe configuration of the E-PHICH.

1) Embodiment 3-1

A BS may report which channel between a PHICH and an E-PHICH is used foreach subframe to transmit ACK/NACK for the PUSCH through an RRC message.A PHICH monitoring configuration and an E-PHICH monitoring configurationmay be performed in the same subframe as that used in a PDCCH monitoringconfiguration and an E-PDCCH monitoring configuration, respectively.

2) Embodiment 3-2

Alternatively, a selection of a PHICH and an E-PHICH may be determinedaccording to a DCI format used as a UL grant. For example, the PHICH maybe used for a PUSCH scheduled with a DCI format 0, and the E-PHICH maybe used for a PUSCH scheduled with a DCI format 4. A UE may implicitlyknow which channel between the PHICH and the E-PHICH is used to receiveACK/NACK on the DCI format included in the UL grant.

3) Embodiment 3-3

A selection of a PHICH and an E-PHICH may be indicated by using a bitfield combination of a UL grant. For example, a specific state of a DMRSfield may be allowed to indicate a use of the E-PHICH.

4) Embodiment 3-4

If a UL grant for a corresponding HARQ process is transmitted, theE-PHICH may not be transmitted. Therefore, upon detection of a UL grant,even if there is a resource allocated to the E-PHICH, the UE may ignorethis and use the resource as a PDSCH.

Fourth Embodiment

Designation of a PHICH cell/subframe or an E-PHICH cell/subframe.

Embodiment 4-1

If a UL grant exists in a PDCCH, a PDCCH cell (or subframe) is a PHICHcell (or subframe), and if the UL grant exists in an E-PDCCH, an E-PDCCHcell (or subframe) may be an E-PHICH cell (or subframe).

Embodiment 4-2

For each cell in which a PUSCH is transmitted, a BS may configure adesignation of a PHICH monitoring cell and an E-PHICH monitoring cell toa UE through an RRC message. That is, the BS may report which channelbetween a PHICH and an E-PHCH is used to transmit ACK/NACK through anRRC message for each cell in which the PUSCH is transmitted.Alternatively, which channel between the PHICH and the E-PHICH is usedto transmit ACK/NACK for the PUSCH may be configured through the RRCmessage for each subframe in one cell. That is, the UE monitors acorresponding channel according to a configured state.

Embodiment 4-3

A PHICH may be used in case of a UL HARQ process scheduled with a PDCCH,and an E-PHICH may be used in case of a UL HARQ process scheduled withan E-PDCCH.

The aforementioned third embodiments and the fourth embodiments may beused in combination.

<Configuration of E-PHICH>

An E-PHICH may be configured with an independent channel different froma PDCCH or an E-PDCCH similarly to a relation of PDCCH-PHICH.

Alternatively, the E-PHICH may be transmitted in a DCI format of theE-PDCCH. In this case, it may be transmitted by performing CRCscheduling thereon by using an E-PHICH identifier which is allocated foreach UE group by multiplexing HARQ ACK for a plurality of UEs (such asan identifier is called an E-PHICH-RNTI). Alternatively, only for a UEwhich transmits a PUSCH, a compact DCI format including ACK/NACK withoutresource allocation information or scheduling information such as NDI,MCS, DMRS, etc., (information such as TPC or the like may be included)may be transmitted by performing CRC scheduling with a C-RNTI allocatedto the UE. Such a compact DCI format may be transmitted with the samelength as a DCI format 0/1A, thereby being able to avoid an increase ofblind decoding. If a UL transmission mode is a mode in which up to 2codewords can be transmitted, it may be configured such that 2-bitACK/NACK is received or spatially bundled ACK/NACK is received.

If a PUSCH transmission UL subframe corresponding to a DL subframe inwhich an E-PHICH is transmitted is two or more in number in a time orfrequency domain (this may occur in a TDD UL-DL configuration 0 or mayoccur when scheduling a plurality of cells in an E-PHICH transmissioncell), the following method may be applied.

1) When applying DCI with CRC-scrambled E-PHICH-RNTI.

An E-PHICH-RNTI scrambled to a DCI format in which ACK/NACK is includedfor each subframe or cell may be configured separately. Alternatively, acompact DCI format including ACK/NACK may be identified according to avalue I_(PHICH) or a CIF.

Alternatively, one E-PHICH-RNTI may be applied to all of DCI formatsincluding ACK/NACK.

2) When applying DCI with CRC-scrambled C-RNTI.

All PHICHs corresponding to one compact DCI format may be configured andtransmitted.

If a PHICH is transmitted with one DCI, a mapping order of a PHICH bitfield may be arranged in an ascending order of a CIF according to a mostsignificant bit (MSB), or starting from a DL subframe which is advancedtemporally, or in an ascending order of a codeword number.

When applying the E-PHICH-RNTI, UEs for sharing this may be allowed tosearch a common search space to read the same resource. For this, aconfiguration of a search space for detecting DCI scrambled with theE-PHICH-RNTI may be determined on the basis of the E-PHICH-RNTI or maystart at a pre-determined value (E-CCE index=0).

If a specific E-PDCCH group is used to transmit the DCI scrambled withthe E-PHICH-RNTI, in order to avoid an increase in the number of blinddecoding attempts, detecting of a DCI format 0/1A (this is a commonformat which exists in all transmission modes) may not be attempted.Alternatively, the DCI scrambled with the E-PHICH-RNTI may be detectedonly in a specific search space.

If one of E-PDCCH sets is dedicatedly used for transmission of DCIscrambled with the E-P-PHICH-RNTI, blind decoding may be performed todetect the DCI scrambled with the E-PHICH-RNTI by the number of times ofattempting the blind decoding used only in a corresponding set.

If the E-PHICH is configured for DCI detection, the number of times ofattempting the blind decoding for a corresponding cell may be increased.In case of the existing secondary cell, blind decoding is performed onlyin a UE-specific search space. However, if there is a need to detect theDCI scrambled with the E-PHICH-RNTI, the number of times of attemptingthe blind decoding for this may be added.

Meanwhile, in case of an NCT in which a PHICH is not configured,non-cross carrier scheduling (i.e., self-scheduling) may be not allowed,and only non-cross carrier scheduling in an LCT may be allowed. Toimplement this, the existing CRS-based PDCCH transmission may not beperformed in the NCT. In addition, the E-PDCCH may not be configured inthe NCT.

Which one is used among the methods may be signaled through RRC.

<PHICH or E-PHICH Selection and Cell Selection in Carrier AggregationBetween Multiple Sites>

In carrier aggregation, a plurality of cells (carriers) used by one BSmay be aggregated, or respective carriers used by different BSs, e.g., amacro BS and a small BS, may be aggregated. The latter may be carrieraggregation between a plurality of sites. In the carrier aggregationbetween the plurality of sites, an operation of a case where a PHICH isnot present in a cell in which a PUSCH is transmitted may be appliedwith extension to an operation of a case where the PHICH is not presentin a site including the cell in which the PUSCH is transmitted.

Meanwhile, if a delay of a backhaul is great between sites, due to atime delay of information sharing between cells, transmission of adynamic scheduling control channel and transmission of a data channelmay be configured independently for each site. In this case, if a PHICHof an LCT is utilized, it may be configured to use a PHICH resource ofthe LCT in a site in which a PUSCH is transmitted.

In addition, for the use of the E-PHICH, the E-PHICH is also configuredin a cell of the same site and is utilized. Therefore, even if there isan LCT more suitable for another site, instead of utilizing it, theE-PHICH is configured in the same site, or a PHICH-less operation isconfigured.

In addition, even if data is transmitted through UL/DL split betweensites, a control channel is configured in a site in which the data istransmitted. That is, even if a cell A of a site 1 transmits data byutilizing only DL and a cell B of a site 2 transmits data by utilizingonly UL, control information (e.g., a DL grant, a PUCCH) of the cell Amay be transmitted through the UL of the cell A, and control information(e.g., a UL grant, an (E)PHICH) of the cell B may be transmitted throughthe DL of the cell B.

<Method of Configuring PHICH Resource>

In a future wireless communication system, a plurality of componentcarriers are used for communication using a wider band, or a structureof an independent area consisting of resource blocks transmitted onlythrough a data channel without a control channel is proposed for aneffective use of a system resource.

FIG. 10 shows an example of a structure of a carrier including asegment.

The segment may be a frequency band which does not provide backwardcompatibility. For example, the segment may be a band in which a controlchannel is not included.

In case of LTE, one subframe consists of 12 or 14 OFDM symbols, and oneor more of the OFDM symbols are used for control channel transmission. Aregion used for the control channel transmission is called a PDCCHregion. The PDCCH region uses a resource allocation scheme having acontrol channel element (CCE) structure. On the other hand, a regionused for data channel transmission is called a PDSCH region. The PDSCHregion uses a resource allocation scheme having a resource blockstructure. A region indicated by B in FIG. 10 may conform to theLTE(Rel-8)-based channel structure and resource allocation scheme.

In case of an LTE-A UE supporting LTE-A, an LTE-A dedicated frequencyband may be configured for the purpose of transmitting data in a greateramount in comparison with an LTE case or because of a restrictioncondition of a center frequency interval. In FIG. 10, a band denoted byS₀ and S₁ may be an LTE-A dedicated frequency band. In this case, asystem band recognized by an LTE UE is different in size from a systemband recognized by an LTE-A UE as shown in FIG. 10, and thus a PRB indexinterpreted by the LTE UE may also be different from that of the LTE-AUE.

For convenience of explanation, it is assumed hereinafter that an A-bandis greater than a B-band, and the A-band includes the B-band. In thiscase, a UE which recognizes the B-band is called a type-B UE, and a UEwhich recognizes the A-band is called a type-A UE. That is, a UE whichrecognizes the A-band consisting of the B-band recognized by the type-BUE and additional bands that cannot be recognized by the type-B UE (thebands are called segments, for example, S₀ and S₁ of FIG. 10) is calledthe type-A UE.

In the legacy PHICH, as expressed by Equation 2, a mapping relation isconfigured sequentially with a resource block index of a PUSCH, and a UEcan know which PHICH resource is used to transmit ACK/NACK by a BS byapplying an offset value signaled with a PHICH index corresponding to alowest resource block index I^(lowest) ^(_) ^(index) _(PRB) _(_) _(RA)of an allocated PUSCH.

Meanwhile, since there is a restriction conventionally in that an uplinkband cannot be configured to be greater than a downlink band, thedownlink band can be regarded as a maximum value of the uplink band. Thetotal number of PHICH resources is determined by applying a parameter Ngwith respect to the downlink band, and thus it is impossible to extendthe PHICH resource by considering an extended uplink band due to asegment band. Therefore, a shortage of the PHICH resource may occur.Hereinafter, it is proposed a method of configuring a PHICH resource fora PUSCH scheduled in a segment band by a type-A UE when there aredifferent types of UEs.

<Order Arrangement Method of PUSCH Resource Block Index>

As described in Equation 2, a PHICH resource is determined on the basisof a PRB index of corresponding PUSCH transmission. If theaforementioned segment is aggregated and used in the legacy LTE carrier,how to index a PUSCH resource block in the aggregated carrier may be amatter to be considered.

FIGS. 11(A)-11(D) show an example of PUSCH indexing methods.

First Embodiment

Referring to FIG. 11(A), indexing is achieved starting from a lowfrequency as to the entirety of an A-band. When applying this method, anindex of a B-band is recognized differently between a type-B UE and atype-A UE.

That is, the type-A UE recognizes that an index of a resource block ofthe B-band is from 10 to 27, whereas the type-B UE recognizes that theindex is from 0 to 17. Therefore, a complexity occurs in PHICH indexcollision avoidance.

Further, there may be a need for a method in which the conventionalequation is applied by subtracting resource blocks having a lower indexthan a B-band from indexing of SRS and PUCCH resources and thereafterthe subtracted resource blocks are compensated and mapped. Meanwhile,there is an advantage in that continuous PUSCH resources can beallocated to a B-band and an S-band by using one UL grant.

An index of the B-band may be maintained in initial access, and a newindex may be applied after the S-band is allocated at a later time.

Second Embodiment

Referring to FIG. 11(B), an index of a B-band is maintained withoutalteration, and an index of an added S-band is assigned subsequently toan index the B-band. An order of assigning an index between addedS-bands may start from a low frequency band, or may conform to signalingfrom a BS. In each band, indexing may be performed starting from a lowfrequency. As such, if the index of the B-band is maintained withoutalteration, the entire scheduling of the A-band is possible with one ULgrant, but there is a disadvantage in that resource allocation isachieved discontinuously. However, there is an advantage in that anoperation in the existing band can be maintained.

Third Embodiment

Referring to FIG. 11(C), an index of a B-band is maintained withoutalternation, and an index of an added S-band is newly assigned. An orderof assigning an index between added S-bands may start from a lowfrequency band, or may conform to signaling from a BS. In each band,indexing may be performed starting from a low frequency.Disadvantageously, scheduling of a B-band and an S-band cannot beperformed with one UL grant.

Fourth Embodiment

Referring to FIG. 11(D), an index of a B-band is maintained withoutalternation, and an index of an added S-band is newly assigned for eachS-band. In each band, indexing may be performed starting from a lowfrequency. Disadvantageously, each of split S-bands also has to use a ULgrant.

The first embodiment to the fourth embodiment may be selected andcombined for use.

If PUSCH indexing of FIG. 11 is used, a collision of a PHICH resourcemay occur. To avoid this, a cyclic shift based on a value n_(DMRS)included in a UL grant may be adjusted. N^(group) _(PHICH) and n^(seq)_(PHICH) may be given by Equation 3 below.n _(PHICH) ^(group)=(I _(PRB) _(_) _(RA) +n _(DMRS))mod N _(PHICH)^(group) +I _(PHICH) N _(PHICH) ^(group)n _(PHICH) ^(seq)=(└I _(PRB) _(_) _(RA) /N _(PHICH) ^(group) ┘+n_(DMRS))mod 2N _(SF) ^(PHICH)  [Equation 3]

In Equation 3 above, n_(DMRS) is mapped from a cyclic shift of a DMRSfield included in the latest PDCCH which includes an uplink DCI formatfor a transport block related to corresponding PUSCH transmission. Ifthe PDCCH including the uplink DCI format does not exist and a firstPUSCH is scheduled with SPS or if the first PUSCH is scheduled by arandom access response grant, n_(DMRS) is set to 0.

In Equation 3, I_(PRB) _(_) _(RA) may be given by Equation 4 below.

                             [Equation  4]$I_{PRB\_ RA} = \left\{ \begin{matrix}I_{PRB\_ RA}^{lowest\_ index} & \begin{matrix}{{for}\mspace{14mu}{the}\mspace{14mu}{first}\mspace{14mu}{TB}\mspace{14mu}{of}\mspace{14mu} a\mspace{14mu} P\; U\; S\; C\; H\mspace{14mu}{with}} \\{{associated}\mspace{14mu} P\; D\; C\; C\; H\mspace{14mu}{or}\mspace{14mu}{for}\mspace{14mu}{the}\mspace{14mu}{case}} \\{{of}\mspace{14mu}{no}\mspace{14mu}{associated}\mspace{14mu} P\; D\; C\; C\; H\mspace{14mu}{when}\mspace{14mu}{the}} \\{{number}\mspace{14mu}{of}\mspace{14mu}{negatively}\mspace{14mu}{acknowledged}} \\{{TBs}\mspace{14mu}{is}\mspace{14mu}{not}\mspace{14mu}{equal}\mspace{14mu}{to}\mspace{14mu}{the}\mspace{14mu}{number}\mspace{14mu}{of}} \\{{TBs}\mspace{14mu}{indicated}\mspace{14mu}{in}\mspace{14mu}{the}\mspace{14mu}{most}\mspace{14mu}{recent}} \\{P\; D\; C\; C\; H\mspace{14mu}{associated}\mspace{14mu}{with}\mspace{14mu}{the}} \\{{corresponding}\mspace{14mu} P\; U\; S\; C\; H}\end{matrix} \\{I_{PRB\_ RA}^{lowest\_ index} + 1} & \begin{matrix}{{for}\mspace{14mu} a\mspace{14mu}{second}\mspace{14mu}{TB}\mspace{14mu}{of}\mspace{14mu} a\mspace{14mu} P\; U\; S\; C\; H} \\{{with}\mspace{14mu}{associated}\mspace{14mu} P\; D\; C\; C\; H}\end{matrix}\end{matrix} \right.$

I^(lowest) ^(_) ^(index) _(PRB) _(_) _(RA) denotes a lowest PRB index ina first slot of corresponding PUSCH transmission.

FIG. 12 shows an example of configuring an uplink band when a bandincluding a segment is configured as a downlink band.

Referring to FIG. 12, the segment may be applied only to a downlink, andin an uplink case, only an uplink band recognized by a type-B UE may beused. In order to decrease an adjacent band's interference which occursby a resource block added with the segment, it is necessary to use amore accurate RF filter, which may result in an increase in a cost ofthe UE. Therefore, it may be advantageous to apply such a method.Relatively, a cost increase caused by the more accurate RF filter maynot be a significant burden to a BS. In case of the type-A UE in TDD, aDL subframe may be recognized as a resource block allocable band untilan A-band, and a UL subframe may be recognized as a resource blockallocable band only until a B-band.

Alternatively, in a downlink case, a PDCCH, a CRS, etc., are present,and thus there is a need to identify a compatible band and a segmentband, whereas in an uplink case, it is not necessary to identify them.In this case, an uplink band may be allocated with the same size to thetype-B UE and the type-A UE. This may be applied limitedly only to FDDsince the type-B UE may recognize a downlink band and an uplink banddifferently in TDD.

<When Applying E-PHICH or Applying PHICH-Less Operation>

When an S-band is configured, a PHICH resource of the existing B-bandmay be insufficient if an increase of a resource block is great. Forthis, an E-PHICH may be used, or a retransmission method based on a ULgrant without a PHICH response may be used. It may be applied to a casewhere the S-band is allocated or a case where a lowest index of a PUSCHbelongs to the S-band when the S-band and the B-band are commonlyallocated. Alternatively, it may be applied to a UE which uses theentirety of the A-band.

<When Using Different UL-DL Configurations or when Using Different FrameStructures in Aggregation of LCT and NCT>

In case of using a PHICH of the existing LCT as to a PUSCH of an NCT nothaving an E-PHICH, it is applicable if the NCT and the LCT use the sameTDD UL-DL configuration and the same frame structure. Herein, in theLCT, cell-specific UL-DL configuration information is delivered throughSIB1, and if the LCT is aggregated with a secondary cell, thecell-specific UL-DL configuration information is RRC-signaled when thesecondary cell is added/modified. On the other hand, since SIB 1 may notbe transmitted in the NCT, information which is RRC-signaled is thecell-specific UL-DL configuration information.

However, when using an aggregation between the NCT and the LCT usingdifferent TDD UL-DL configurations or an aggregation between a TDD celland an FDD cell, a cell for transmitting a PHICH and a cell fortransmitting a PUSCH may have different PUSCH HARQ timings, and thusthere may be a case where a PHICH resource is not configured in some DLsubframes of a PHICH cell. As a method for avoiding such a problem, thefollowing method may be applied.

1) In the aggregation between the LCT and the NCT, PUSCH transmissionmay not be achieved in the NCT. For this, in case of the FDD, a ULcarrier may not be linked to an NCT DL carrier. In case of the TDD, a ULsubframe corresponding to the NCT DL subframe may not be configured(e.g., only a DL subframe may be used in a UL-DL configuration). Inother words, in the NCT cell, only a DL carrier/subframe may beconfigured instead of configuring a UL carrier/subframe.

2) In the aggregation of the LCT and the NCT, an aggregation betweencarriers having different UL-DL configurations or different framestructures (e.g., an aggregation between a TDD carrier and an FDDcarrier) may not be allowed. Such a restriction may be applied only to acarrier aggregation combination which may have a case in which a PHISCHresource is not configured in some DL subframes of a PHICH cell fortransmitting a PHICH.

3) A PHICH-less operation is applied to a case where a PHICH resource isnot configured in some DL subframes of a PHICH cell not transmitting thePHICH. The PHICH-less operation implies that retransmission/newtransmission is performed only by using a UL grant for scheduling thesame cell. For this, a UE reports ACK to a higher layer by assuming thatthe ACK is transmitted through a PHICH in a subframe in which the ULgrant is not received. In this case, PUSCH retransmission is deferred.

4) The E-PHICH may be used for a case where a PHICH resource is notconfigured in some DL subframes of the PHICH cell for transmitting thePHICH.

5) In case of aggregating carriers having different UL-DL configures ordifferent frame structures in the aggregation between the LCT and theNCT, only cross-carrier scheduling may be allowed, and the PHICH cellfor transmitting the PHICH may be configured as a cell in which a ULgrant is transmitted. The cross-carrier scheduling may be limited to aprimary cell.

6) If carries using different UL-DL configurations are aggregated in theaggregation between the LCT and the NCT and if non-cross-carrierscheduling (based on an E-PDCCH) of the NCT is performed, instead of arule (conforming to a cell-specific reference PUSCH HARQ timing of asecondary cell) used in the non-cross-carrier scheduling between the LCTand the LCT, a reference timing of the cross-carrier scheduling betweenthe LCT and the LCT may be applied to the secondary cell (i.e., NCT).

If carriers having different frame structures are aggregated in theaggregation between the LCT and the NCT and if non-cross-carrierscheduling (based on an E-PHCCH) of the NCT is performed, instead of arule used in non-cross carrier scheduling between the LCT and the LCT, areference timing of the cross-carrier scheduling between the LCT and theLCT may be applied to a secondary cell (i.e., NCT). For example, it mayconform to a PUSCH HARQ timing of a primary cell.

If carriers having different frame structures are aggregated whenaggregating a plurality of LCTs and a plurality of NCTs and if non-crosscarrier scheduling of the NCT (based on an E-PDCCH) is performed, aPHICH cell may be restricted to use the same frame structure or the sameUL-DL configuration.

Table 6 below shows a DL subframe in which a PHICH exists in a TDD UL-DLconfiguration and FDD.

TABLE 6 UL-DL Configura- Subframe number n tion 0 1 2 3 4 5 6 7 8 9 0 HH H H 1 H H H H 2 H H 3 H H H 4 H H 5 H 6 H H H H H FDD H H H H H H H HH H

In Table 6 above, H denotes a DL subframe in which a PHICH exists.

An aggregation of the LCT and the NCT may be allowed only for a casewhere all of DL subframes of the LCT corresponding to DL subframesdenoted by H in the NCT have a UL-DL configuration/frame structure inwhich a PHICH exists (e.g., when the NCT has a UL-DL configuration 4 andthe LCT has a UL-DL configuration 3).

It may be restricted such that the LCT having the UL-DLconfiguration/frame structure including all DL subframes denoted by H inthe NCT is selected as a PHICH cell.

If a cell using a UL-DL configuration 0 is a PHICH cell in theaforementioned methods, there is a case where PHICH resources areallocated twice in amount so that the resources are respectively mappedto two UL subframes (resources are identified by I_(PHICH)=0,1). In thiscase, one of I_(PHICH)=0,1 may be set as a default value. For a loaddistribution, the value I_(PHICH) may be applied for each carrier index(CI). For example, I_(PHICH)=1/0 may be mapped according to whether theCI is an odd number/even number. This may also occur in the combinationof the LCT and the LCT, and the same may also be applied thereto.

In case of aggregating carriers having the same TDD UL-DL configurationand the same frame structure, a method of effectively utilizing theexisting resource without a problem in utilizing a PHICH of the LCT maybe applied. However, there may be a problem if the method is applied inother cases. Therefore, as to the NCT, it is effective to selectivelyapply the method of utilizing the legacy PHICH and the method of notutilizing the legacy PHICH. The selection may use a pre-determinedscheme according to a cell combination or may be performed through RRCsignaling.

<Starting Position of E-PDCCH in Cell for Receiving PHICH>

In case of using the legacy PHICH without an E-PHICH, the legacy PHICHduration has an effect on a PDCCH region. Therefore, an OFDM symbol spanof the PDCCH region depending on the PHICH duration must be consideredwhen configuring an E-PDCCH region. In particular, if an OFDM symbolstarting position of the E-PDCCH is configured on the basis of a PCFICH,when configuring the PCFICH, it may be configured dynamically byconsidering the PHICH duration.

In case of a cell in which a UE does not read the PHICH, the OFDM symbolstarting position of the E-PDCCH is designated with RRC, and in case ofa cell in which the UE reads the PHICH, the OFDM symbol startingposition of the E-PDCCH may be determined in such a manner that aPCFIDCH is detected to confirm a span of a PDCCH region, and a start ofan E-PDCCH region may be recognized starting from a next OFDM symbol.This is because PCFICH reception may be reliable in case of the cellcapable of reading the PHICH.

However, even for the cell capable of reading the PHICH, the followingmethod may be considered when the OFDM symbol starting position of theE-PDCCH is configured with RRC. The same may also be applied when anOFDM symbol starting position of the PDSCH is determined.

For example, it may be applied to an operation performed when the PDSCHis received in CoMP. Further, if the E-PHICH is configured in acorresponding subframe, it may be equally applied to a case ofdetermining the OFDM symbol starting position of the E-PHICH.

The starting position of the E-PDCCH or the PDSCH may start from asecond OFDM symbol or may start from a first OFDM symbol. If it startsfrom the second OFDM symbol, it is applied only to a case of an extendedPHICH duration. If it starts from the first OFDM symbol, it is alsoapplied to a case of a normal PHICH duration.

1. If the OFDM symbol starting position of the E-PDCCH is configuredwith RRC, a value greater than a PHICH duration D_(PHICH) is configured.That is, if the PHICH duration is 2, the OFDM symbol starting positionof the E-PDCCH is configured to a symbol which comes after a third OFDMsymbol of a subframe. If a start OFDM symbol index of the E-PDCCH (it isassumed that a first OFDM symbol index is 0) is S_(E-PDCCH) _(_) _(RRC),it is set to S_(E-PDCCH)=S_(E-PDCCH) _(_) _(RRC)≧D_(PHICH).

2. If a reference value for configuring the OFDM symbol startingposition of the E-PDCCH is configured with RRC, a maximum value betweenthe PHICH duration D_(PHICH) and a value S_(E-PDCCH) _(_) _(RRC)configured with RRC is used. That is, S_(E-PDCCH)=max(S_(E-PDCCH) _(_)_(RRC), D_(PHICH)).

For example, in a case where the PDDCH is sufficiently configured withtwo OFDM symbols whereas a PHICH duration requires 3 OFDM symbols, whichis greater than 2 OFDM symbols, an E-PDCCH region and a region of aPDSCH scheduled with an E-PDCCH may be effectively configured in asubframe in which a PHICH is not present.

That is, when D_(PHICH)=3, if it is set to S_(E-PDCCH) _(_) _(RRC)=2 byconsidering a case where a PHICH is not present, a subframe in which thePHICH is not present may use a third OFDM symbol as an E-PDCCH or aPDSCH.

FIG. 13 shows a method of determining a starting position of an E-PDCCH.

Referring to FIG. 13, a UE receives PHICH duration information throughsystem information (step S110). The PHICH duration information mayindicate D_(PHICH).

The UE receives an RRC message indicating the starting position of theE-PDCCH (step S120).

The UE determines the starting position of the E-PDCCH using the PHICHduration information or the RRC message according to whether a PHICHexists in a subframe (step S130).

If the PHICH exists in the subframe, a start OFDM symbol of the E-PDCCHis determined according to a greater value between the PHICH durationinformation and the starting position of the E-PDCCH indicated by theRRC message. On the other hand, if the PHICH does not exist in thesubframe, the starting position of the E-PDCCH is determined accordingto the RRC message.

For example, the PHICH duration information and the RRC message may havedifferent values such as a case where D_(PHICH)=3 and starting positioninformation (S_(E-PDCCH) _(_) _(RRC)) of the E-PDCCH indicated by theRRC message is set to 2. Therefore, the starting position of the E-PDCCHfor each subframe may vary depending on a presence/absence of the PHICH.Accordingly, a resource can be more effectively used in comparison witha case where the starting position of the E-PDCCH is reported with theRRC message irrespective of the presence/absence of the PHICH.

Table 7 shows subframes in which a PHICH does not exist in a TDD UL-DLconfiguration. Subframes indicated by D are subframes in which the PHICHdoes not exist.

TABLE 7 UL-DL Configura- Subframe number n tion 0 1 2 3 4 5 6 7 8 9 0 1D D 2 D D D D D D 3 D D D D 4 D D D D D D 5 D D D D D D D D 6

Meanwhile, instead of a scheme of determining a starting position of anE-PDCCH (or PDSCH) by avoiding OFDM symbols in which a PHICH istransmitted, data mapping of the E-PDCCH and the PDSCH may be puncturedor rate-matched in an REG region occupied by the PHICH.

In this case, if transmission of the E-PDCCH and the PDSCH requires anRE-pair of a frequency axis or a time axis similarly to a case ofSFBC/STBC, even if one RE in the RE pair collides with an REG occupiedby the PHICH, rate-matching is performed on both of them. For example, acase of using the SFBC may be a case of being scheduled with a DCIformat 1A.

<An Operation when a PDSCH Region Collides with a Region (RB) Configuredas a PHICH Transmission Region>

When a UE is scheduled for a PDSCH of a specific cell, the followingoperation may be performed in a DL subframe in which the PDSCH isscheduled.

1. When a PDSCH of the DL subframe overlaps with an E-PHICH region, thePDSCH is prioritized. That is, it is recognized that the E-PHICH regionis not used.

2. A BS performs scheduling such that the PDSCH does not overlap withthe E-PHICH region.

3. In case of the PDSCH, a region configured as the E-PHICH isunconditionally punctured or rate-matched. If a UE can recognize thatonly a part of the region configured as the E-PHICH is used for the UE,only the part may be punctured or rate-matched.

The method 3 may be applied only to a case of a PDSCH scheduled withouta DL grant. For example, it may be applied only to a case where the BStransmits the PDSCH through DL SPS or the PDSCH is transmitted throughbundled subframe scheduling. Hereinafter, for convenience, only SPS isused for explanation. If the DL grant exists, the BS may performscheduling so as to avoid a collision of the PDSCH and the E-PHICHregion, whereas if the PDSCH is scheduled with SPS without the DL grant,it may be inevitable to avoid the collision. Therefore, the method 3 isapplied in this case.

If scheduling is performed with SPS, the following method may beapplied.

When resource blocks including an E-PHICH region are allocated by usinga normal DL grant, if an E-PDCCH region is punctured or rate-matched inthe resource blocks, a puncturing or rate-matching operation shall notbe performed on a region which collides with the E-PHICH region of a DLsubframe in which a PDSCH is scheduled without a corresponding DL grantby using SPS scheduling. That is, the colliding region is recognized asa PDSCH transmission region. The puncturing implies that data ispunctured after being carried on a corresponding region. Therate-matching implies that data is not carried on a corresponding regionbut is carried on the remaining regions to adjust to a transfer rate.

A subframe in which such an operation is performed may include orexclude a subframe in which a PDCCH/E-PDCCH indicating SPS activation istransmitted. In addition, it may be selectively applied according towhether a control channel indicating SPS activation is transmittedthrough the PDCCH or through the E-PDCCH. That is, when performing SPSscheduling, the scheduling is performed so that a collision does notoccur with the E-PHICH.

In addition, in a subframe for receiving an E-PHICH (i.e., a subframe inwhich a UE previously performs PUSCH transmission and a BS transmits acorresponding E-PHICH), if a PRB including a resource occupied by theE-PHICH overlaps with the PDSCH, the PRB may be rate-matched orpunctured by excluding a PDSCH allocation. In this case, if the PDSCH isscheduled without the E-PDCCH on another subframe scheduled with theE-PDCCH on the subframe (e.g., bundled subframe scheduling or SPSscheduling), the PDSCH may be used equally to a PDSCH scheduled on asubframe which is the same as that used in the E-PDCCH. That is, thePDSCH may be used by excluding the PRB which includes the resourceoccupied by the E-PHICH in the scheduled subframe.

In addition, in an E-PDCCH, if a PRB including an E-REG/E-CCE occupiedby DCI of the E-PDCCH (including an SPS activation E-PDCCH) forscheduling a PDSCH (and/or PUSCH) overlaps with the PDSCH, the PRB maybe rate-matched or punctured by excluding PDSCH allocation. In thiscase, if the PDSCH is scheduled without the E-PDCCH on another subframescheduled with the E-PDCCH, the PDSCH may be used equally to a PDSCHscheduled on a subframe which is the same as that used in the E-PDCCH.That is, the PDSCH may be used by excluding the PRB which includes theE-REG/E-CCE occupied by the DCI.

Such a method has an aspect of maintaining a code rate for a case ofinitial scheduling and an aspect of preparing for a case where a UEmisses a corresponding region when the region is a PRB preferably usedto transmit DCI to the UE and when the region has a high possibility ofbeing used again in DCI transmission.

The aforementioned methods may be respectively applied when aconfiguration location of the E-PHICH exists in an E-PDCCH region inwhich a CSS is configured and an E-PDCCH region in which a USS isconfigured. For example, a CSS region may use the method 3, and a USSregion may use the methods 1 and 2. Alternatively, the methods may beapplied only to an E-PDCCH set in which the E-PHICH is configured.Alternatively, the methods may be applied only to an E-PDCCH type(distributed E-PDCCH, localized E-PDCCH) in which the E-PHICH isconfigured. Preferably, the E-PDCCH may be configured in the distributedE-PDCCH. That is, the same is also applied to a case of the E-PDCCH.

This may conform to a relation between the E-PDCCH and the PDSCH. Theaforementioned operation of E-PHICH and PDSCH may use the same technicalfeature as that applied to the relation between the E-PDCCH and thePDSCH.

<Restriction on Subframe Configured for E-PHICH>

There is a restriction on a subframe or PRB that can be configured for acase of E-PDCCH. For example, the following cases are possible in LCT.

1) A special subframe in which PDSCH transmission is not performed.

Special subframe configurations #0 and #5 for a normal CP and specialsubframe configurations #0 and #4 for an extended CP are applied herein.The special subframe configuration may be found in the section 4.2 of3GPP TS 36.211 V8.6.0 (2009-03).

2) A subframe in which all E-CCEs are mapped to an RB in which a DM RSis not transmitted.

Examples thereof include a special subframe configuration #7 for anextended CP, an E-PDCCH set in which all E-CCEs overlap withPBCH/PSS/SS, etc.

3) A subframe in which some E-CCEs are mapped to a PRB in which a DM RSis not transmitted: A corresponding PRB when an RB allocated withE-PDCCH overlaps with an RB in which PBCH/PSS/SSS is transmitted.

A UE may assume that there is no E-PHICH transmission in a subframe inwhich an E-PDCCH is not transmitted, or in a subframe in which a part ofthe E-PDCCH is not transmitted, or in a corresponding PRB. That is, theUE does not attempt E-PHICH detection in a corresponding subframe.

Such a subframe restriction may be selectively applied according to eachE-PDCCH set in which an E-PHICH is configured, each type, or the likesimilarly as described above. In this case, regarding a UL HARQ processcorresponding thereto, the legacy PHICH may be used or a PHICH-lessoperation may be used.

FIG. 14 shows a structure of a BS and a UE according to an embodiment ofthe present invention.

A BS 100 includes a processor 110, a memory 120, and a radio frequency(RF) unit 130. The processor 110 implements the proposed functions,procedures, and/or methods. For example, the memory 120 is coupled tothe processor 110, and stores a variety of information for driving theprocessor 110. The RF unit 130 is coupled to the processor 110, andtransmits and/or receives a radio signal.

A UE 100 includes a processor 210, a memory 220, and an RF unit 230. Theprocessor 210 implements the proposed functions, procedures, and/ormethods. For example, the memory 220 is coupled to the processor 210,and stores a variety of information for driving the processor 210. TheRF unit 230 is coupled to the processor 210, and transmits and/orreceives a radio signal.

The processors 110 and 210 may include an application-specificintegrated circuit (ASIC), other chipset, a logic circuit, a dataprocessing device, and/or a converter that converts a baseband signaland a radio signal to each other. The memories 120 and 220 may include aread-only memory (ROM), a random access memory (RAM0, a flash memory, amemory card, a storage medium, and/or other storage device. The RF units130 and 230 may include one or more antennas that transmit and/orreceive the radio signal. When the embodiment is implemented bysoftware, the aforementioned technique may be implemented by a module (aprocess, a function, and the like) that performs the aforementionedfunction. The module may be stored in the memories 120 and 220 and maybe executed by the processors 110 and 210. The memories 120 and 220 maybe present inside or outside the processors 110 and 210 and connectedwith the processors 110 and 210 by various well-known means.

What is claimed is:
 1. A method of receivingacknowledgement/not-acknowledgement (ACK/NACK) of a terminal in awireless communication system, the method comprising: transmittinguplink data through an uplink data channel, wherein the uplink datachannel is transmitted through aggregated carriers; and receivingACK/NACK for the uplink data, wherein the aggregated carriers include afirst band recognizable to first and second type of terminals and asecond band recognizable only to the second type of terminal, andwherein resource blocks included in the first band are indexed in orderusing a first index, and a second index is used for indexing resourceblocks included in the second band.
 2. The method of claim 1, wherein aresource constructing a downlink channel for receiving the ACK/NACK isdetermined on the basis of a resource block having a lowest indexconstituting the uplink data channel.
 3. The method of claim 1, whereinthe resource blocks included in the first band are indexed in the sameindexing order applied to the first type of terminal which operates onlyin the first band.
 4. The method of claim 1, wherein the first type ofterminal supports only an operation in the first band, and the secondtype of terminal supports operations in the first band and the secondband.
 5. A communication method of a terminal in a wirelesscommunication system, the method comprising: receiving physicalhybrid-ARQ indicator channel (PHICH) information indicating a timeduration of a downlink channel for receivingacknowledgement/not-acknowledgement (ACK/NACK) through systeminformation; and receiving information indicating a starting position ofan enhanced-physical downlink control channel (E-PDCCH) through a radioresource control (RRC) message, wherein an orthogonal frequency divisionmultiplexing (OFDM) symbol at which the E-PDCCH starts is determined onthe basis of a greater value between the PHICH information andinformation indicating a starting position of the E-PDCCH.
 6. The methodof claim 5, wherein the E-PDCCH is a control channel located in a regionto which a data channel is allocated.
 7. The method of claim 5, whereinan OFDM symbol at which the E-PDCCH starts is determined on the basis ofa smaller value between the PHICH information and information indicatinga starting position of the E-PDCCH.
 8. A terminal comprising: a radiofrequency (RF) unit for transmitting and receiving a radio signal; and aprocessor, operatively coupled to the RF unit, that: controls the RFunit to transmit uplink data through an uplink data channel, wherein theuplink data channel is transmitted through aggregated carriers; andcontrols the RF unit to receive acknowledgement/not-acknowledgement(ACK/NACK) for the uplink data, wherein the aggregated carriers includea first band recognizable to first and second type of terminals and asecond band recognizable only to the second type of terminal, andwherein resource blocks included in the first band are indexed in orderusing a first index, and a second index is used for indexing resourceblocks included in the second band.